Solution styrene butadiene rubbers (SSBR) are synthetic products consisting of butadiene and styrene unit made by solution polymerization method. Industrial production of the solution SBR was first proposed by the U.S. company, Phillips, in batch process and Firestone company in continuous process. Since the solution SBR is superior to the emulsion SBR (ESBR) in mechanical properties and rolling resistance, the solution SBR is widely used by the automotive industry and in other rubber products.
With the increasing requirements for cars with low fuel economy, demands on tire rubber materials for such characteristic requirements also increase. Conjugated diene based rubbers with low rolling resistance, excellent wear resistance, and balanced wet-skid resistance provide excellent steering stability, leading to the increase in demand. On the other hand, the industry has proposed to add silica compounds or mixture of silica compounds and carbon black as a reinforcing agent to a rubber composition. Tire treads containing compounds with mixture of silica and carbon black or silica compounds are favorable with low rolling resistance and wet-skid resistance, so as to provide excellent steering stability.
In order to achieve a better bond between the conjugated diene rubber and the reinforcing agent, the industry has developed lots of techniques for modified conjugated diene rubber. Of the related technical publications, U.S. Pat. No. 4,185,042 discloses a coupling agent used for SBS block copolymer. Lithium-containing polymer reacts with the silicon-containing coupling agent, thereby obtaining the SBS block copolymer with the coupling ratio >90% and no Si—OR group presented in the SBS block copolymer. U.S. Pat. No. 5,219,938 discloses a two-stage modification process. By using two kinds of modifiers, the chain ends of lithium-containing diene polymer molecules react with the coupling agent RnSiCl4-n or RnSnCl4-n to perform a first modification, and then with the coupling agent, R5R6R7—Si—(CH2)n—N—R8R9, to perform a second modification. U.S. Pat. No. 7,288,594 discloses a two-step modification of lithium-containing styrene-butadiene rubber by using two different kinds of silane compounds. In addition, U.S. Pat. No. 7,807,747 discloses a two-step modification of lithium-containing styrene-butadiene rubber by using same silane compound.
However, the processes of the above-mentioned related arts are mostly complicated and difficult to practice. Therefore, there is a need of a novel modification technique for conjugated diene rubber to overcome the problems of conventional arts.